Effect Of Cu And Ce Elements On Microstructures And Mechanical Properties Of Al-7Si-0.35Mg Alloys

Al-7Si-0.35Mg alloy can be reinforced by heat treatments. The productionprocess of this alloy is simple. The tensile strength of this alloy is poor. Coarseacicular silicons in the casting structures affect the strength and toughness of thematerial, and the application of this material is limited.In the present work, theinfluence of Cu, Ce and heat treatment on microstructures and mechanical propertiesof Al-7Si-0.35Mg alloys were investigated by using the control variables. This paperprovides a reference to further improve the Al-Si alloy mechanical properties. The keyfindings are as follows:1. When Cu content is3.4-3.8%, the tensile strength of T6state Al-7Si-0.35Mgalloy increases by more than50%. It increases with the increasing of Cu content, upto395.7MPa. When the Cu content exceeds3.8%, the tensile strength begins todecline. When Cu content is3.8-4.0%, the elongation of T6state alloy decreases27%than of the alloy added3.6%Cu.2. Ce can modify the lath eutectic silicon in cast alloy into short rod, coral-like,and finally tiny granules. After the heat treatment, the elongation of alloy with0.15%Ce increased by76%than the alloy without Ce element. Ce content exceeding0.15%,the tensile strength and elongation of the T6state alloy falls with the increasing of Cecontent. Adding more than3.6%Cu and more than0.30%Ce to Al-7Si-0.35Mg alloys,needle-shaped Al9Ce2Cu5Si3phases emerged. The multi-phase cannot be eliminatedby the heat treatment. It has an adverse effect on the tensile strength and theelongation of alloys.3. Increasing Cu content, the corrosion resistance of Al-7Si-0.35Mg alloysdecreases. After heat treatment, the corrosion rate of the alloy added3.6%Cu has asmall difference with the alloy added3.4%Cu, it only increases5%. Cu contentexceeding3.6%, the corrosion rate of the heat treated alloy significantly faster. Afteradding0.15%Ce, the corrosion rate of Al-7Si-0.35Mg-3.6Cu alloy has the lowestvalue. After adding more than0.15%Ce, the corrosion rate of the alloy increases.From what has been discussed above, under our experimental conditions, the betterdosage of Cu, Ce element in Al-7Si-0.35Mg alloy is3.6%and0.15%, respectively.4. For the Al-7Si-0.35Mg-3.6Cu-0.15Ce alloy, the optimization of the heattreatment is solution at505℃for12hours and then aging at160℃for10hours. After aging, Al-7Si-0.35Mg-3.6Cu-0.15Ce alloy brinell hardness increase by72%,tensile strength is403Mpa and elongation is7.9%. In cast structure, Cu and Cesegregates in the grain boundary. After solution treatment, majority of they solution tothe (Al) matrix, and evenly distributed. Al2Cu phase dispersedly precipitates duringaging, playing an effect of precipitation strengthening. The fracture mode of this alloychanges from brittle fracture to quasi-cleavage fracture.5. The tensile strength of T6state Al-7Si-0.35Mg-3.6Cu-0.15Ce alloy is410MPa,the elongation of this alloy is9.6%. As casted alloys, the Brinell hardness of l owpressure casting Al-7Si-0.35Mg-3.6Cu-0.15Ce alloys increased by9%than of gravitycasting alloys, the tensile strength increased by5.5%and the elongation increased byabout32%. After heat treatment, the tensile strength and elongation of low pressurecasting alloys were higher than gravity casting alloys, the elongation of low pressurecasting alloys increased about19%than of gravity casting alloys.